Upon reaching the top floor of the Intex tower, walk up to the door and Gessler will open it on you temporarily knocking you out. He will advance toward you can draw his gun, but before he can shoot you, jump over his head to the ceiling and then maneuver behind him. Rewire the camera to the door, and then make a powerful leap onto Gessler pushing you both through the door into the camera's view. The door will slam on both of you, incapacitating Gessler and leaving Conway stunned briefly.